Vehicle assistance systems, such as vehicle guidance and accident prevention systems, of the prior art detect electromagnetic signals from the road. For example, U.S. Pat. No. 5,684,490 to Young et al. discloses a highway vehicle guidance system which transmits radar pulses forward of the vehicle. Such pulses are reflected back by a frequency selective strip for detection by a radar receiver. The reflected radar pulse signals are analyzed to guide the vehicle along the highway. Similarly, U.S. Pat. No. 5,318,143 to Parker et al. discloses a lane sensing system which includes an optical transmitter for emitting a light toward a highway lane. The light reflected from a center stripe is analyzed for automatic vehicle steering. In addition, U.S. Pat. No. 5,568,137 to Liu includes a photo sensor mechanism for detecting light that is reflected from light-reflective lane markers for alerting the driver that the vehicle may be deviating out of a lane.
These prior art vehicle assistance systems transmit and/or detect electromagnetic waves. Such transmitters and detectors may be costly to implement. Furthermore, analysis of such electromagnetic waves may require relatively complicated signal analysis, especially for optical systems when background light may vary from day-time to night-time. Moreover, the electromagnetic waves may be difficult to detect because of scattering of the electromagnetic waves in foggy, rainy, or snowy weather, and the strips and lines used in these systems may become completely undetectable during heavy fog, or heavy rain, or even light snow accumulation on the road. However, the driver of the vehicle may require most assistance, especially accident prevention assistance, during such adverse weather conditions. In addition, the reflective strips or lines used in these prior art vehicle assistance systems may wear out with time.
U.S. Pat. No. 5,555,312 to Shima et al. discloses an automobile apparatus that recognizes road traffic lines and a car running ahead of a vehicle from a video image recording unit such as a TV camera mounted on the car. However, such a video image recording unit and video image signal processing may be relatively costly to implement. Moreover, this system also may become ineffective in adverse weather conditions of heavy fog, rain, or even light snow.
Other vehicle assistance systems of the prior art include embedding magnetic keys on the road and detecting the resulting magnetic field with magnetic sensors installed on the vehicle. However, the magnetic sensors and installation of magnetic keys on the road may require relatively high cost. In addition, installation on the road of such magnetic keys or the frequency selective strips of Young et al. may be useless for vehicles that do not have the corresponding vehicle assistance system installed thereon.
Furthermore, some prior art vehicle assistance systems combine the prior art detection technology as described herein with navigation technology using GPS (Global Positioning System) information and/or roadmap information. However, such vehicle assistance systems are limited by navigation precision and the ability to receive GPS signals.